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Comb drive
Comb drive
Combdrive is a MEMS device that utilize electrostatic forces acting between two electrically conductive combs connected to the voltage source.
Problem Type: electrostatics.
Geometry: 3D extrusion.
Comb thickness L_{z} = 40 um.
Gap d = 2.5 um.
Given:
Relative permittivity of air ε = 1,
Relative permittivity of comb ε = 10,
Potential difference ΔU = 40 V
Problem:
Find the attraction force per tooth width and compare with 2D analytical solution:^{*}
F = 0.5 · εε_{0} · n·L_{z} · U^{2} / d,
where n is number of air gaps.
Solution:
The simulation model includes only one pair of teeth (two air gaps, n=2). The Dn=0 boundary condition is applied on the plane of symmetry.
Results:
Analytical solution (force per one pair of electrodes, n=2):
F = 0.5 · 1 · 8.854e12 · 2·40e6 · 40^{2} / 2.5e6 = 2.27e7 N.

Force F 
Analytical solution 
2.27e7 N (88%) 
2D plane simulation 
2.29e7 N (89%) 
3D extrusion simulation 
2.59e7 N (100%) 
^{*} Comb drive, from Wikipedia, the free encyclopedia.
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